Front End Acetylene Hydrogenation

[Ahmed Mohamed 90]

Hello. I'm junior engineer working in a ethane cracking facility with back end acetylene hydrogenation. Currently, I am requested to prepare a study over the process of front end acetylene hydrogenation. How the hydrogenation is controlled and so, pros and cons compared to backend type.

Anyone can help me with data?

 

[georgeverghese]

In the naphtha cracker plant drawings I have, the C2H2 hydrogenation unit treats the raw combined ethane - ethylene stream from the de ethanizer tops, which I presume is what you call back end hydrogenation ?

Where would the front end unit be located - upstream of primary or upstream of secondary de methanizer ?

 

[Ahmed Mohamed 90]

Front end if the feed is before the chilling train, primarily C2- (C1,C2s,Hydrogen and CO). For tail end, the feed to reactor is after the chilling train, after the separation of C1 and H2. And you can control the amount of Hydrogen and CO fed to the reactor via separate control loops for each.

 

[georgeverghese]

Though I am not an expert on the pros and cons for various configurations for C2H2 hydrogenation, I suspect there is a higher risk that valuable propylenes and propadienes may also get hydrogenated in the upstream reactor option, while this cannot happen in the tail end setup. These heavier olefins and dienes will drop out into the bottoms product from the ethane - ethylene fractionator in this tail end setup.

Upstream of the primary demethanizer, C3 components will all be mostly still in the vapor phase.

There are more details on the effect of H2 and CO on the selectivity for acetylene hydrogenation with Pd - Ag catalysts in this article wrt to reactor location, which you may wish to download

Maximise ethylene gain and acetylene selective hydrogenation efficiency

Third-generation stabilised front-end selective acetylene hydrogenation catalysts provide high selectivity, low sensitivity to CO swings and slow deactivation

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